Heatingpannel 750 watt breadth 340 mm / altitude 440 mm / weight 3,4 kg The formula for calculating the required capacity judging by cubic meters is as follows: Number of cubic meters delta to heat (lxbxa) x T x heat insulation factor the delta T is the difference between the outside temperature and the desired surroundings temperature (therefore at -5 outside and desired temperature of 20 is the delta T: 25 the heat insulation factor space isolated for a good is 1.2. For a moderately isolated space that factor 2 is and for a badly isolated space is that 3.3. Therefore: a moderately isolated space of 5.5 x 20 meters and 4 meters high with an outside temperature of -5 and desired within temperature of 18 would ask will sit a capacity of 20.2 kW... at border cases rather always something higher (therefore 850W becomes 1000W).